1. Field of the Invention
The present invention relates to a numerical controller for controlling a machine tool, and more specifically to a numerical controller having a function of drive-controlling each axis on the basis of data stored in the form of a table.
2. Description of Related Art
A numerical controller that allows the free movement of a tool without being constrained by commands in blocks as in conventional technology and enables a reduction in machining time and high precision in machining by prestoring the motion amount and position of each axis in the form of a table and drive-controlling each axis according to the data stored in the table, instead of by commands in blocks of an NC program, has been publicly known.
For example, there is a well-known invention that prestores the position of a movable axis by time or by rotation angle as numerical control data, monitors time or rotation angle, and output the numerical control data corresponding to the movable axis every time the stored time or rotation angle is reached (see JP 59-177604A).
In another well-known invention, there is provided a data table for storing the commanded positions of X-axis and Z-axis with respect to reference positions. A value of a counter for counting reference pulses is multiplied by an override value to obtain the reference positions. Based on the reference positions, the commanded positions of the X-axis and Z-axis stored in the data table are outputted to synchronously control the X-axis and the Z-axis. By so doing, even if the drive control is performed by the data stored in the data table, an override can be used. It is also possible to give a command for linear connection between the commanded positions, quadratic-function connection, cubic-function connection or the like, and to give a command for auxiliary functions (see JP 2003-303005A).
FIGS. 8 to 10 are schematic views of operations by table data (hereinafter referred to as path-table operation), which is disclosed in JP 2003-303005A and has conventionally been performed.
In the example illustrated in FIG. 8, there are provided an X-axis path table Tx and a Z-axis path table Tz. FIG. 9 shows an example of the X-axis path table Tx, and an X-axis position is stored in relation to a reference variable. FIG. 10 is a graph showing the X-axis position moved according to the X-axis path table Tx shown in FIG. 9.
In the same manner, a Z-axis position is stored in the Z-axis path table Tz in relation to a reference variable. Moreover, a pulse from a position encoder fixed to the spindle (spindle position) or a reference pulse based on time from a reference external pulse generating section is inputted into a counter 1 to be counted. An override value set by override means is multiplied by the counted value of the counter 1 using a multiplier 2 and is stored in a reference variable counter 3. The reference variable counter 3 is reset at the time point when the path-table operation is commanded. Values of the reference variable counter 3 are inputted as reference positions into X-axis and Z-axis path table interpolation processing sections 4x and 4z. The X-axis and Z-axis path table interpolation processing sections 4x and 4z obtain commanded positions of the X-axis and Z-axis with respect to the reference positions, referring to the X-axis path table Tx and the Z-axis path table Tz, and obtain motion amounts in a processing cycle to output the motion amounts to control axis motors 5x and 5z as commands. The X-axis and the Z-axis are then synchronously operated according to the reference positions.
When the path-table operation is carried out by a multi-axis and multi-system lathe or the like, because the reference time or spindle position is common in a conventional numerical controller, the machining by the path-table operation cannot be performed in systems individually. The machining therefore has to be executed after the processing of another system is finished. Additionally, when the path-table operation is performed in a certain system, it is impossible to execute an operation by regular NC statements in another system.